incidental fixes to .ins importer

Author: briantoby

GSASII/imports/G2phase_INS.py

@@ -26,15 +26,16 @@ def ContentsValidator(self, filename):
             if l.startswith('CELL'):
                 break
         else:
-            self.errors = 'no CELL record found'
-            self.errors = 'This is not a valid .ins file.'
+            self.errors = 'no CELL record found. '
+            self.errors += 'This is not a valid .ins file.'
             fp.close()
             return False
         fp.close()
         return True
 
     def Reader(self,filename,filepointer, ParentFrame=None, **unused):
         'Read a ins file using :meth:`ReadINSPhase`'
+        self.MPhase = None
         self.Phase = self.ReadINSPhase(filename, ParentFrame)
         return True